At the same time, the organization representing the state’s doctors said it has dropped a push to change federal regulations and remove marijuana from a list of the most dangerous drugs — a classification that some scientists cite as an obstacle to the research.

“Given this information, it’s time for medical and scientific communities to develop large-scale clinical trials to determine whether marijuana is safe and effective as a medical intervention,”Aghababian wrote Friday on the society’s website. “Such research should identify all the treatment protocols that would apply to a standard pharmaceutical therapy, including indications, contraindications, dosages, length of therapy, side effects, and more.”

But the people trying to do exactly that work say the Schedule I classification does get in their way.

Aghababian cites the work of a California research center led by Dr. Igor Grant. With state funding and access to the only federally-sanctioned supply of marijuana, that center has conducted a series of small studies that have found marijuana relieved pain in patients with HIV or other conditions and eased muscle stiffness in people with multiple sclerosis.

“The classification of marijuana as a Schedule I drug as well as the continuing controversy as to whether or not cannabis is of medical value are obstacles to medical progress in this area,” the researchers wrote.

Rick Doblin of Belmont, executive director of the Multidisciplinary Association for Psychedelic Studies, said the real obstacle to research is not the drug’s classification but limits on access to the federal drug supply — he called it a monopoly by the National Institute of Drug Abuse, aided by the DEA.

The association has been working for 12 years with a University of Massachusetts professor to try to establish another facility in which to grow marijuana in the controlled setting that research requires. The DEA denied the professor’s application for a facility license in 2009, a decision he is appealing in federal court.

The medical society does not plan to respond to the DEA letter, spokesman Rick Gulla said.

“The letter satisfies our concern,” Gulla said. “We still must recognize that marijuana has a potential for abuse and is prohibited under federal law.”